1. Field of the Invention
The present invention relates, in general, to a method for making an electrode of a secondary lithium cells and, more particularly, to a method for making a cathode of a secondary lithium cell by co-precipitating lithium and cobalt ions at a predetermined ion ratio in an alkaline solution.
2. Description of the Prior Art
A lithium secondary cell typically comprises a lithium metal or carbon for anode, a chalcogenide compound or transition metal oxide for cathode, and an organic solvent for electrolyte. The material for the cathode should exhibit chemical stability to the electrolyte, charge/discharge reversibility and high energy density. In particular, a lithium ion cell which employs carbon as an anode requires a cathode material high in unit cell voltage. For this, transition metal oxides are selected, including LiCoO.sub.2, LiNiO.sub.2, LiNi.sub.1-y Co.sub.y O.sub.2 and LiMn.sub.2 O.sub.4. Depending on the kind of materials, such as lithium and transition metal salts, and on the thermal conditions therefor, the oxides could greatly affect the properties of the cell, such as, for example, discharge capacity and cycle life span.
Most of the methods known to those skilled in the art are of solid state reaction in which the lithium salts and the transition metal salts are thermally treated at a temperature of 400-1000.degree. C. (Japanese Pat. Laid-Open Publication No. Heisei 7-262994). The powder obtained by the solid state reaction, however, requires a temperature too high for thermal treatment and too much time for calcination in addition to being inhomogeneous in size and irregular in morphology.
In order to exhibit superior electrode properties even at high current density, the powder used as a material for lithium secondary cells should be homogeneous in size and regular in morphology. To use LiCoO.sub.2 as an electrode material for lithium secondary cells, it is made into a powder. There has been developed no method, except for a solid state reaction technique, to make LiCoO.sub.2 electrodes exhibiting excellent properties, thus far.